Question

So, this might be a little bit messy for me to explain, but here it goes.

I have, what i think are, numbers stored in core data and i am trying to convert them into strings so that i can use them as labels for table cells, maybe dumb but please bear with me.

I pump the core data items into an array and am trying to get them back out, i run a FOR loop and use this code to make a number for each item.

NSNumber *num = [arr objectAtIndex:i];

When i run, i get no errors and if i log them i get everything returned as expected. However, if i run this afterwards program force quits.

NSString *myOutput = [num stringValue];

I believe it is because what ever i actually have and am pulling out is not really a number therefore it cannot be made into a string using stringValue, anyone know a way to test for what an object is? Maybe using NSLog some how?

Also side question. In a FOR loop where i create objects I need to remember to release them each time the loop is run correct?

Thanks so much!

Answer 1

There’s a few ways of checking what objects contain or whether they are of a certain type; either the

[myObject class];

check – if you break on a line after it you can see the class. With your NSNumber though, it will either be a number or have nothing inside it, ie

if (myNSNumber != nil)
    // then it must hold a value

Finally, there is this test – also perfectly viable:

if ([myProbableStringObject isKindOfClass:[NSString class]])
    // then let's do something with it

Also yes – you should release objects created in your for loop for best memory management and code efficiency. Hope this helps 🙂